Are you referring to a retirement plan like a 401(k)?
The distribution to you should have been reported on a 1099-R that should have been mailed to you or made available on the retirement plan administrator's website.
The gross distribution and the amount of federal income tax withheld will both be on the form.
To enter this in TurboTax, please do a Search (upper right) for 1099-r (lower case) and click on the jump-to link (Mac users must look for 1099-R in the Topics List). You will be able to enter the 1099-R data there.
If this is not what you meant, please come back and tell us.
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